1. Field of the Invention
The present invention relates to the field of photography and, more specifically, to self-developig cameras having structuure for influencing the distribution ofprocessing composition within a self-developing film unit.
2. Description of the Prior Art
An important step in the processing of a self-developing film unit is the distributing of the fluid processing composition between a predetermined pair of adjacent layers of the film unit, subsequent to exposure, to initiate a development and diffusion transfer process. In order to optimize that process, the fluid must be uniformly distributed over the entire photoexposed area of the film unit.
The present invention relates to controlling the distribution of a processing fluid within an integral or "nonpeel apart" self-developing film unit, representative examples of which are disclosed in U.S. Pat. No. 3,415,644 and 3,594,165.
Basically, these integral film units are multilayer structures having a rupturable container, holding a fluid process composition, at a leading end thereof and a trap for collecting excess fluid at the trailing end. The multilayer structure includes a pair of outer support sheets, at least one being transparent, and a plurality of layers including photosensitive and image receiving layers sandwiched between the outer support sheets which are bound together along lateral edges thereof.
Subsequent to exposure of the photosensitive layer or layers through the outer transparent sheet, the film unit is advance, leading end first, between a pair of pressure applying member for applying a compressive pressure progressively along the length of the film unit thereby rupturing the container, discharging the fluid between a predetermined pair of adjacent layers and distributing the fluid.
Because the layers are bound together along the lateral edges thereof, there is more resistance to fluid flow adjacent these edges than in the center portion of the film unit. Consequently, the discharged mass of fluid tends to advance rearwardly along a tongue-shaped wavefront with a greater concentration of fluid in the center than out at the lateral edges.
In order to compensate for the initial uneven distribution of fluid, it has been found to be advantageous to selectively apply a second compressive pressure to the central portion of the film unit in the path of the rearwardly advancing wavefront. The compressive pressure forces part of the fluid away from center and toward the lateral edges.
U.S. Pat. No. 3,779,770 discloses a film container having integrally formed distribution control surfaces or projections thereon for selectively applying the second compressive pressure to the film unit as it is advanced through a film withdrawal slot in the container to the pressure applying members. Also, reference may be had to U.S. Pat. NO. 3,820,137 which disclose a self-developing camera having structure for engaging and deflecting a thin wall portion of the film container having the distribution members formed therewith for positively urging the control members into engagement with the center portion of a film unit being advanced through the film withdrawal slot.
The integral self-developing film units generally have an inherent stiffness and as a film unit progressively advances from the exit side of the pressure-applying members, in cantilever fashion, it tends to follow a natural and substantially planar path of travel which is defined by the inherent stiffness. It has been discovered that by deflecting the film unit from the natural path of travel, thereby inducing a gentle and large radius bend in the film unit on the exit side of the pressure-applying member, that the uniformity of distribution of fluid within the film unit is significantly and beneficially influenced.
While it is well estabalished that the uniformity of fluid distribution is enhanced by inducing a bend in the film unit as it emerges from the pressure-applying members, the mechanisms which produce the beneficial effect are not well defined at the present time.
A self-developing camera having structure for inducing a bend in the film unit as it emerges from the pressure-applying members is disclosed in U.S. Pat. No. 3,810,211 issued to R. R. Wareham on May 7, 1974. The camera is of the compact, folding, single lens reflex type and includes a housing section which extends forwardly of a pair of pressure-applying members. A combination film bending or deflecting plate and light shielding member is mounted near the forward end of the housing section adjacent a film exit slot therein that is out of alignment with the natural or normal path of travel of the film unit. The plate is mounted for movement between a folded position and an extended position wherein it is disposed in the emerging path of travel for deflecting the emerging film unit, to induce the beneficial bend or curvature, and guiding it to the film exit slot. The disclosed housing section is characterized by its conventional construction using a plurality of piece parts that must be sequentially assembled and adjusted to define the film exit slot and mount the deflecting plate in predetermined relationship with respect to the pressure applying members and exit slot.